JPH1058308A - Polishing device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a polishing device capable of performing a polishing process, with the distribution of bearing pressure kept in an optimum state over polished surface, by controlling the posture of a top ring for holding a workpiece. SOLUTION: A polishing device is equipped with a turntable 2 having polishing surface 1 and a top ring 3 to hold a workpiece W, and polishes the workpiece W, with both of the turntable 2 and the top ring 3 rotated for causing the sliding motion of the polishing surface 1 and the polished surface of the workpiece W. Regarding the polishing device so formed, a magnetic bearing device 10 for holding the rotary shaft 12 of the top ring 3 on a thrust bearing 13 and radial bearings 14 and 15 is provided, together with a posture control means to control the posture of the top ring 3 relative to the turntable 2 via the control of a magnetic bearing.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a polishing apparatus, and more particularly, to a polishing apparatus that supports a rotating shaft of a top ring with a magnetic bearing.

[0002]

2. Description of the Related Art In recent years, as the degree of integration of semiconductor devices has increased, circuit wiring has become finer and the distance between wirings has become smaller. Especially in the case of optical lithography of 0.5 μm or less, the depth of focus becomes shallower. Therefore, the flatness of the image forming surface of the stepper is required. Further, if particles larger than the distance between the wirings exist on the substrate, problems such as short-circuiting of the wirings occur. Therefore, in the processing of the substrate, it is important to clean the substrate together with the flattening. Such a situation is the same in the process of processing a glass substrate used as a mask or the like or a substrate such as a liquid crystal panel.

As a conventional polishing apparatus, as shown in FIG. 10, a turntable 2 having a cloth (polishing cloth) 1 attached to an upper surface thereof, and a top ring 3 for holding a workpiece (semiconductor wafer) W are provided. doing. The turntable 2 and the top ring 3 are provided with a driving device for rotating each of them independently, and a biasing device such as an air cylinder for pressing the two together is provided.

[0004] In such a polishing apparatus,
The edge of the workpiece W is the turntable 2
The turntable 2 and the top ring 3 are independently rotated while the polishing liquid Q is supplied from the nozzles 4 while the polishing liquid Q is being supplied so as to be located at a predetermined distance from the center and the edge of the wafer W. Polish the entire surface uniformly.

The top ring 3 is a disc-shaped member having a holding surface on the lower side for holding an object to be polished W by suction or the like, and its connecting portion with the support shaft 5 has a universal joint structure using balls 6. I have. Thereby, the top ring 3 tilts in accordance with the force from the turntable 2 side during polishing, and absorbs the influence of the alignment error between the turntable 2 and the top ring 3 and the local fluctuation of the polishing cloth, thereby achieving stable polishing. Can be performed.

[0006]

However, in the above-mentioned prior art, the top ring 3 is unnecessarily tilted with respect to the polishing surface by the action of the ball 6, and the polishing surface (cross surface of the turntable 2) is turned. ) And the surface to be polished of the object W to be polished become non-uniform, and there is a problem that a uniform polishing amount cannot be obtained. This point will be discussed in more detail in relation to the operation between the workpiece W held by the top ring 3 and the polishing cloth 1 of the turntable 2.

In the polishing apparatus, the polishing amount is
It can be expressed by the following equation. Qp = η × P × V × T Polishing amount: Qp Proportional coefficient: η Surface pressure: P Relative speed: V (Relative speed between wafer polishing surface and turntable) Polishing time: T Therefore, as one of the above elements, Uniform pressure in the plane is also one of the main conditions for making the polishing amount uniform.

However, as schematically shown in FIG. 11A, a frictional force f is generated between the polishing surface on the independently rotating turntable and the surface to be polished on the lower surface of the top ring (f = μN), which generates a moment force M around the sphere 6. As a result, the top ring 3 is tilted as shown in FIG. 2B, and a phenomenon that the object to be polished "pushes" into the surface layer of the polishing cloth 1 occurs in the front portion in the polishing direction shown in FIG. The inclination angle θ is naturally determined by the action of the ball 6 according to the relationship between the pressing force N and the frictional force f, as shown in FIG.

Then, as shown in FIG. 1D, the inclination θ causes an uneven surface pressure distribution such that the pressure in this portion is increased, and the workpiece W is also rotated.
The distribution is as shown in FIG. An appropriate surface pressure distribution for obtaining a uniform polishing amount also depends on conditions such as the elasticity of the polishing cloth and the inflow state of the polishing liquid. Therefore, it is not sufficient that the angle θ is 0. However, as in the above case, the angle θ determined by the action of the ball 6 as a result of the action of the various forces acting on the top ring is also not necessarily the angle that provides an appropriate surface pressure distribution for obtaining a uniform polishing amount. is not.

In the conventional method, since the angle is determined by the action of the ball 6 as a result of the action of various forces acting on the top ring, the angle fluctuates depending on local conditions of the polishing surface, and stable polishing conditions are obtained. It may not be possible, and may even cause vibrations and further instability. As a result, as shown in FIG. 11E, the polishing amount is larger on the outer edge side than on the center side, and a uniform polishing amount cannot be obtained.

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and is intended to perform polishing by controlling the attitude of a top ring holding an object to be polished so that the surface pressure distribution on the surface to be polished is in an optimum state. It is an object of the present invention to provide a polishing apparatus which can perform polishing.

[0012]

According to a first aspect of the present invention, there is provided a turntable having a polished surface, and a top ring for holding a polished object. In a polishing device for polishing by sliding the surface to be polished, a magnetic bearing device that supports the rotation axis of the top ring by a thrust bearing and a radial bearing,
A polishing apparatus, further comprising: attitude control means for controlling the attitude of the top ring with respect to the turntable by controlling the magnetic bearing.

[0013] By controlling the attitude of the top ring holding the object to be polished by applying the control mechanism of the magnetic bearing, the surface pressure distribution on the surface to be polished is optimized and the polishing is performed. High polishing can be performed.

According to a second aspect of the present invention, the attitude control means controls an inclination angle of the polished surface and the polished surface along the traveling direction of the turntable.
A polishing apparatus according to (1). If the polished surface has no elasticity like a grindstone, good results can be obtained if the polished surface and the polished surface are completely parallel during polishing. When the polished surface is formed of a material having a certain degree of elasticity, such as a polishing cloth, the optimum inclination angle varies depending on various factors such as surface pressure and relative polishing speed.

Usually, the inclination angle between the polished surface and the polished surface along the traveling direction of the turntable is controlled. The angle setting is set to an angle that avoids the “thrust” or an angle that cancels out the force received by the “thrust” so that the surface pressure of the lower surface of the top ring becomes uniform as a result. The inclination angle of the top ring can be easily controlled by setting a position command value of the magnetic bearing control system based on a polishing test in advance. That is, the inclination angle is
Control can be performed based on displacement signals from displacement sensors of the thrust bearing and the radial bearing of the magnetic bearing device.

The inclination angle may be set in advance based on a polishing test. In addition, the inclination angle,
The control may be performed based on displacement signals from displacement sensors of the thrust bearing and the radial bearing of the magnetic bearing device.

The invention according to claim 3 is the polishing apparatus according to claim 1, further comprising controlling a surface pressure between the polishing surface and the surface to be polished. Thus, the polishing can be performed while maintaining the surface pressure value itself in addition to the surface pressure distribution at an appropriate value using the magnetic bearing. The surface pressure can be estimated from each load current.
Further, the surface pressure may be controlled by controlling the exciting current of the thrust bearing. Further, the surface pressure may be controlled by controlling an elevating mechanism for moving the magnetic bearing device up and down. By setting the surface pressure in advance based on a polishing test, relatively easy control can be performed.

According to a fourth aspect of the present invention, a turntable having a polished surface and a top ring for holding the object to be polished are used to slide the polished surface and the polished surface of the object to be polished while rotating them. In the polishing method of moving and polishing, the rotating shaft of the top ring is supported by a magnetic bearing device having a thrust bearing and a radial bearing, and the attitude of the top ring with respect to the turntable is controlled by controlling the magnetic bearing. The polishing method is characterized in that:

According to a fifth aspect of the present invention, there is provided a turntable having a polished surface, and a top ring for holding the object to be polished, and sliding between the polished surface and the surface to be polished while rotating both. In a polishing apparatus for polishing by
A magnetic bearing device that supports a rotation shaft of the top ring with a thrust bearing and a radial bearing, and a surface pressure control unit that controls a surface pressure between the polished surface and the polished surface by controlling the magnetic bearing is provided. A polishing apparatus.

The surface pressure may be estimated from each load current. Further, the surface pressure may be controlled by controlling an exciting current of the thrust bearing. Also in this case, the surface pressure may be set in advance based on a test.

According to a sixth aspect of the present invention, a turntable having a polished surface and a top ring for holding an object to be polished are used to slide the polished surface and the polished surface of the object to be polished while rotating both. In the polishing method of moving and polishing, the rotating shaft of the top ring is supported by a magnetic bearing device having a thrust bearing and a radial bearing, and the surface between the polished surface and the polished surface is controlled by controlling the magnetic bearing. This is a polishing method characterized by controlling the pressure.

[0022]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows a polishing apparatus according to the present invention, in which a cloth (polishing cloth) 1 or a turntable 2 on which a grindstone is stuck on a top surface, and a top ring 3 for holding a workpiece (semiconductor wafer) W. Is provided. The turntable 2 is provided with a drive device (not shown) for rotating the turntable 2 independently of the top ring 3.

The top ring 3 is supported by a magnetic bearing mechanism 10. That is, the rotating shaft 12 of the top ring 3 is disposed inside the casing 11 of the magnetic bearing mechanism 10, and the thrust bearing 13 and the upper radial bearing 1
4. A lower radial bearing 15 is provided. Further, a thrust displacement sensor 17 for detecting a displacement of the rotating shaft 12 in the thrust direction and radial displacement sensors 18 and 19 for detecting a displacement in the radial direction are provided. Drive motor 20
Is disposed between the upper radial bearing 14 and the lower radial bearing 15, and the magnetic bearing mechanism 10 including the drive motor 20 is attached to an external lifting mechanism 36 by a support arm 16 provided on the casing 11. As such an elevating mechanism, a mechanism such as a feed screw capable of precisely controlling a position or an air cylinder is preferable.

FIG. 2 is an enlarged view of the top ring portion of FIG. 1. The thrust magnetic bearing 13 has a thrust disk 13a fixed to the rotating shaft 12, and a pair of upper and lower coils 21a and 21b fixed to the casing 11. Electromagnet core 1
3b and 13c. The upper and lower radial magnetic bearings 14 and 15 have electromagnet cores 14 a and 15 a disposed inside the casing 11, and are provided with eight magnetic poles 14 c and 15 c protruding toward the rotating shaft 12.
Coils 22, 23 common to a pair of magnetic poles adjacent to each other across the X or Y axis are wound. Also, the rotating shaft 1
2, rotor magnetic poles 14b and 15b are provided at corresponding positions.

Hereinafter, the configuration of the radial magnetic bearing will be described with reference to FIG. The stator of the upper radial magnetic bearing 14 includes an electromagnetic coil 22a on the positive side of the X-axis and a pair of electromagnetic coils 22b disposed on the negative side of the X-axis opposite thereto, and these are individually excited. The balance of these suction forces makes the rotating shaft 12
Is controlled in the X direction. Similarly, a pair of electromagnetic coils 22c and 22d are arranged in the Y direction. A rotor magnetic pole 14 b is provided in a bearing portion of the rotor 12. Similarly, the lower radial bearing 15 includes an electromagnet core 15a including eight magnetic poles 15c, and respective electromagnetic coils 23a, 23b, 23c, and 23d.
Further, a rotor magnetic pole 15b is provided in a bearing portion of the rotor 12.

Reference numeral 17 denotes a thrust displacement sensor for detecting displacement of the rotating shaft 12 in the thrust direction, and reference numerals 18 and 19 denote radial displacement sensors for detecting displacement in the radial direction.
The radial displacement sensor 18 includes a pair of radial displacement sensors 18x arranged opposite to each other in the X direction, and a pair of radial displacement sensors 18y arranged opposite to each other in the Y direction.
The drive motor 20 includes a motor core 20a and a coil 2
0b and a motor rotor core 20c.

FIG. 4 is a block diagram showing a functional configuration of a control unit for controlling the polishing apparatus according to this embodiment. As shown in the drawing, the control unit includes a subtractor 30 and a controller 31. The subtractor 30 detects a floating position target value and a sensor (radial displacement sensors 18, 19, thrust displacement sensor 17) 34, The displacement values x, y, z, of the control target (the rotation axis 12 and the like) converted by the coordinate
alpha, and β is inputted, the difference is the error signal e _x, e _y,
e _z, eα, it is input to the controller 31 as Ibeta. Here, x, y, and z are, as shown in FIG.
The displacements in the axial direction, the Y-axis direction, and the Z-axis direction are shown, α represents the inclination of the X-axis, and β represents the inclination of the Y-axis.

[0028] The error signal _{e x, e y, e z} , eα, eβ is P
ID + receiving the inclination and position control and attenuation processing in a local phase-lead processing section 31-1 further voltage through a notch filter 31-2 for vibration rejection command signal _{v x, v y, v z} , v
is converted to α, vβ. The coordinates are converted into control signals v _xu , v _yu , v _xl , v _yl , v _z of the upper and lower radial magnetic bearings 14, 15 and the thrust magnetic bearing 13 by the coordinate conversion unit 31-3 and supplied to the magnetic bearing drive unit 32. And the signal v
_z is supplied to the surface pressure controller 23.

The magnetic bearing drive unit 32 includes an electromagnetic coil 22a,
22b, 22c, 22d, 23a, 23b, 23c, 2
3d, 21a, 21b and drive circuit 24 for exciting them
It is composed of The signals v _xu , v _yu , v _xl , v _yl ,
v _z is supplied to each drive circuit 24, and in each of the drive circuits 24, the exciting currents I _xu +, I _xu −, and I _xu − for displacing in the positive and negative directions in the radial bearings 14 and 15.
_yu +, I _yu −, I _xl +, I _xl −, I _yl +, I _yl −, and in the thrust bearing 13, I
_z +, I _z −, and the electromagnetic coils 22a, 22b,
22c, 22d, 23a, 23b, 23c, 23d, 2
It is supplied to 1a and 21b to control the attitude of the control object (the rotary shaft 12 and the like).

The surface pressure controller 23 finely adjusts the force of pressing the top ring 3 against the turntable 2. The Z-direction current value signal of the magnetic bearing drive unit 32 and the Z-direction displacement of the sensor 34 are adjusted. And a signal. The output signal of the surface pressure controller 23 is output as a correction signal for the pressing force in the Z direction, as described later, and is added to the signal _Vz by the adder 22 provided after the controller 31.

Next, a method of controlling the polishing apparatus configured as described above will be described with reference to a flowchart. First, the process of the attitude control for controlling the attitude of the top ring will be described with reference to FIG. Here, first, an appropriate value empirically obtained is set as an initial value (st1), and polishing is performed.
(st2). Next, the uniformity of the polished surface is evaluated by an appropriate method, and it is determined whether or not it satisfies a predetermined uniformity condition.
(st3). If this cannot be obtained, reset the settings (st
4) Perform the polishing test again. When an angle satisfying the uniformity condition is obtained at a certain angle of the top ring, main polishing is performed using the angle (st5).

FIG. 9 shows an example of the result of measuring the unevenness of the surface to be polished and evaluating the flatness. In this example, (a) shows the in-plane uniformity of the polishing amount when polishing is performed after setting the optimum angle, and (b) shows the in-plane uniformity of the polishing amount when polishing is performed after setting the angle. The measurement points are shown in FIG. The setting in this case is set under actual polishing conditions. This includes the type of polishing object, the type of polishing liquid, the rotation speed of the turntable and the top ring, the surface pressure described below, and the like.

As described above, the inclination of the rotating shaft 12 is detected by processing the outputs of the radial displacement sensors 18 and 19, and by controlling the inclination of the rotating shaft 12 to an arbitrary angle, the pressing force against the surface to be polished is adjusted. Can be controlled in-plane uniformly.

Next, a surface pressure control step for controlling the value of the surface pressure will be described. As for the surface pressure, an appropriate value is obtained in advance by a test, and this is input as a set value. As shown in FIG. 1, in this example, the pressing pressure of the object to be polished is applied to the casing of the magnetic bearing by a lifting mechanism, which is applied to the polishing surface via a thrust bearing, a rotating shaft, and a top ring. ing. Here, since the thrust bearing receives the reaction force of the pressing pressure against the polished surface, when the pressure on the polished surface fluctuates during polishing, this can be detected from the current value of the thrust magnetic bearing.

The relationship between force and current can be approximated as substantially linear. That is, assuming that K is a coefficient, I is a current value, and F is a force, F = KI, a force is calculated from the above equation, a comparison is made with the set force (pressure), an increase / decrease amount is calculated, and a correction amount is raised / lowered. The position of the entire magnetic bearing is controlled by driving the lifting mechanism up and down to control the pressure on the polished surface. The force to be corrected can be generated by increasing or decreasing the current of the magnetic bearing. In this case, the surface pressure is controlled using the control current of the thrust bearing as a parameter.

FIG. 7 explains the above process as a flow chart. The surface pressure controller 23 detects the control current of the thrust bearing 13 of the drive circuit 24 (st1), and the control current value and the displacement sensor 34 The force acting between the surfaces is calculated from the value of the displacement signal (st2). At this time, if the flying position is constant, the value of K at st2 in the drawing does not change. The calculated surface pressure is compared with a set value (st3), and when it is not within the allowable range, a corrected pressure is calculated (st4). The lifting mechanism is driven based on the calculated correction pressure to control the position of the entire magnetic bearing (st5). And again st
Returning to step 1, the same process is repeated until the difference between the set value and the calculated pressure is within the allowable range. By such control, polishing is performed at a predetermined appropriate surface pressure. This process is illustrated in FIG.

In this case, the control response performance depends on the driving mechanism of the lifting mechanism. When the elevating mechanism is, for example, a ball screw driven by a stepping motor, it is mechanically driven and indirectly controls the pressure. Therefore, the response is not so fast, but it can cope with a slow fluctuation in surface pressure. Instead of the elevating mechanism as described above, the current value for outputting the calculated correction pressure is sent to the thrust bearing, and the current value of the bearing, that is, the pressing force of the top ring shaft is controlled by controlling the force. You may. Changing the current value of the magnetic bearing and changing the pressing pressure on the polished surface means directly controlling the surface pressure without mechanical driving, thereby enabling control with excellent responsiveness.

[0038]

As described above, according to the polishing apparatus of the present invention, the position of the top ring for holding the object to be polished is controlled by applying the control mechanism of the magnetic bearing, whereby the surface of the surface to be polished is controlled. Polishing is performed with the pressure distribution in an optimum state, and polishing with high flatness can be performed.

[Brief description of the drawings]

FIG. 1 is a diagram showing an overall configuration of a polishing apparatus according to the present invention.

FIG. 2 is a diagram illustrating a configuration of a top ring unit of the polishing apparatus of FIG. 1;

3A is a sectional view taken along line AA of FIG. 2, and FIG. 3B is a sectional view taken along line BB of FIG.
It is a figure showing a section.

FIG. 4 is a block diagram illustrating a functional configuration of a control unit that controls a top ring mechanism.

FIG. 5 is a diagram illustrating a relationship among an X axis, a Y axis, a Z axis, an inclination α, and an inclination β.

FIG. 6 is a flowchart illustrating an attitude control step of the polishing apparatus of the present invention.

FIG. 7 is a flowchart illustrating a surface pressure control step of the polishing apparatus of the present invention.

FIG. 8 is a graph showing changes in surface pressure of the polishing apparatus of the present invention.

FIG. 9 is a graph showing the effect of the polishing apparatus of the present invention.

FIG. 10 is a diagram showing the overall configuration of a conventional polishing apparatus.

FIGS. 11A to 11E are diagrams for explaining the operation of a conventional polishing apparatus.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Polishing cloth 2 Turntable 3 Top ring 10 Magnetic bearing mechanism 12 Rotary shaft 13 Thrust bearing 14,15 Radial bearing 31 Controller 32 Magnetic bearing drive

Claims (6)

[Claims] 1. A polishing apparatus comprising: a turntable having a polished surface; and a top ring for holding an object to be polished, wherein the polishing device slides the polished surface and the surface to be polished while rotating the both to polish. A magnetic bearing device that supports a rotating shaft of the top ring with a thrust bearing and a radial bearing; and attitude control means that controls the attitude of the top ring with respect to the turntable by controlling the magnetic bearing. Polishing equipment. 2. The polishing apparatus according to claim 1, wherein the attitude control means controls an inclination angle between the polished surface and the polished surface along the traveling direction of the turntable. 3. The polishing apparatus according to claim 1, further comprising a surface pressure control unit that controls a value of a surface pressure between the polishing surface and the surface to be polished. 4. A polishing method in which a turntable having a polished surface and a top ring for holding an object to be polished are polished by sliding the polished surface and the surface to be polished while rotating both. The polishing method according to claim 1, wherein a rotating shaft of the top ring is supported by a magnetic bearing device having a thrust bearing and a radial bearing, and the attitude of the top ring with respect to the turntable is controlled by controlling the magnetic bearing. . 5. A polishing apparatus, comprising: a turntable having a polishing surface; and a top ring for holding an object to be polished, wherein the polishing device slides the surface to be polished and the surface to be polished while rotating both members. A magnetic bearing device that supports a rotating shaft of the top ring with a thrust bearing and a radial bearing, and a surface pressure control unit that controls a surface pressure between the polishing surface and the surface to be polished by controlling the magnetic bearing. A polishing apparatus characterized by being provided. 6. A polishing method in which a turntable having a polished surface and a top ring holding an object to be polished are polished by sliding the polished surface and the surface to be polished while rotating the both. In the above, the rotating shaft of the top ring is supported by a magnetic bearing device having a thrust bearing and a radial bearing, and the surface pressure between the polished surface and the polished surface is controlled by controlling the magnetic bearing. Polishing method.